128 



Surface orna- 

 mentation. 



Dimensions 

 &c. of valves 

 from Dugahl 

 brook. 



In Assise E 1 d as well as in the others mentioned, the valves are thin 

 and they are flattened on the margins as seen in the shale. Being a thin 

 shell it was more liable to distortion than others occurring with it, 

 excepting perhaps the thin-shelled Leptoboli. 



Sculpture (additional note). The surface of the valves is seldom pre- 

 served except near the beak. A variation from the dull granulated sur- 

 face, where it is well preserved, consist of fine, somewhat irregular con- 

 centric shining ridges; these anastomose irregularly, or at times pass into 

 an irregularly granulated surface. The dorsal valve shows the long callus 

 with the muscle scars sometimes more, sometimes less advanced toward 

 the front. The striae of the cardinal area pass into the depression of the 

 visceral cavity, so that they have no office of articulation, but appear to 

 mark the line of attachment of a ligament or parietal band connecting 

 the back of the two valves ; such ligament or bond must have been 

 divided on the ventral side for the passage of the pedicle. The connec- 

 tion of the two valves seems to have been very like that in Obolua. 



The species exhibits considerable variation in form, as may be gathered 

 from the following table. 



VALVES of Lingulepis Gregwa in Assise E. 1 d., at Dugald brook. 



This table may be compared with the following of valves from another 

 locality. 



